Conventional Wireless sensor networks (WSNs) comprise wireless sensor and actuator nodes that wirelessly communicate with each other enabling different applications such as pervasive healthcare or smart lighting environments. For instance, a medical sensor network (MSN) is a wireless sensor network where patients are equipped with wireless medical sensors (WMSs) that measure, process and forward users' vital signs in real time. Clinical staff can monitor patient's vital signs by means of, e.g., PDAs or bedside monitors.
In this particular context, the provision of basic security services such as entity identification, authentication and access control to wireless sensor networks are essential. Indeed, such a network must be robust and secure enough to prevent attackers from gaining control over the network. General data protection policies such as the European directive 95/46 or healthcare rules such as HIPAA in the United States must be taken into account when designing security systems for MSNs. For instance, only authorized doctors should be able to monitor patient's vital signs.
To enable the network to be robust, the distribution of encryption keys is crucial. These encryption keys are used to establish a secure connection between two nodes, avoiding thus eavesdropping. Thus, key distribution among the nodes is the security's cornerstone as it defines how to distribute the cryptographic keys used to enable those security services. However, the efficient provision of both key distribution and security services is challenging due to the resource-constrained nature of wireless sensor nodes as WMSs in MSNs.
α-secure key distribution schemes (KDSs) have been identified as a feasible and efficient option for key distribution and key agreement in wireless sensor networks such as medical sensor networks (MSN). Here, α designates the security level of the network. These schemes offer a trade-off between scalability, resilience, connectivity, and computational overhead. In α-secure KDSs, nodes do not share ready-made keys. Instead, nodes are provided with some node-specific information that allows them to compute a shared key with any other node in this security domain on input of that node's identifier. This node-specific information is derived from a keying material root (KMRoot) and the node-specific keying material share for node i is denoted by KM(i). Hence, the different keying material shares KM(i) are all different but correlated. This approach is especially interesting for mobile wireless sensor and actuator networks due to different reasons including: (i) its efficiency on resource-constrained wireless sensor nodes; (ii) its feasibility in mobile scenarios such as patient monitoring or wireless control networks addressed by the ZigBee Alliance where both scalability and distributed operation are key features.
However, current state-of-the-art does not specify how to allow for efficient identification and authentication of a node, for instance concerning the aspects entity identification and access control based on α-secure key distribution schemes, and thus, new techniques addressing these problems are required.
Typically, the provision of these security services can be carried out either in a centralized or distributed fashion. When centralized, a central trust center controlling the network security keeps a list of the different entities in the network, their digital identities, and access control rights. When a party A requests a communication with B, both parties rely on the central trust center (TC) to authenticate both parties. The use of a central TC is not convenient for wireless sensor networks as it requires the presence of an online TC, and requires a high amount of communication towards the Trust Center, overloading the Trust Center etc. This is not possible for a resource constrained network like a Zigbee network.
Distributed identification and access control is more adequate for wireless sensor networks, such as MSNs, as it fits their operational requirements: efficiency, minimum delay, no single point of failure. However, usually distributed identification and access control is based on digital certificates and an underlying public-key infrastructure (PKI) based on public key cryptography (PKC); based on various mathematically hard problems (e.g., the integer factorization problem, the RSA problem, the Diffie-Hellman problem or discrete logarithm problem). However, the use of public key cryptography is computationally too expensive for resource-constrained devices such as PDAs or wireless sensor nodes used in this kind of network.